Following the loss of several molars in the left maxilla, a 73-year-old man asked his general dentist practitioner to restore his chewing efficiency. Initially, reconstruction of the left maxilla with an implant supported fixed partial denture was considered. However, intraorally a soft-tissue swelling was observed extending from the midline of the palate to the left buccal sulcus. A panoramic radiograph showed absence of bone between the oral cavity and the maxillary sinus. At first, after an incision biopsy and histopathologic examination, the condition was diagnosed as nodular fasciitis. However, because of subsequent aggressive growth of the lesion malignancy was suspected. Histopathological examination confirmed the assumption. The lesion appeared to be a sarcoma. The general diagnostic rule is that the aggressive behaviour of a lesion and the absence of a bony delineation on radiographic examination between the oral cavity and the maxillary sinus are signs of malignancy, until evidence to the contrary has been provided.